When updating an adaptive digital filter in accordance, for instance, with the LMS-algorithm (Least Mean Square), there is calculated a convergence factor which defines the stop size. In order for the filter to function in the manner desired for different input signals, the step size must be inversely proportional to the signal energy of the filter input signal. When calculating this convergence factor there is therefore a need to divide a constant number by a variable number whose value represents the signal energy. Division operations, however, are often relatively demanding processes and thereby also relatively time consuming.
For instance, an arithmethical division operation according to one known method is performed as a series of repeated, conditional subtractions. The absolute accuracy obtained is proportional to the number of iterations. Arithmethical division operations can also be performed with the aid of equipment that has a relatively large memory capacity. One example in this regard is found described in U.S. Pat. No. 4,707,798, according to which an approximate arithmethical division is effected by table loop-up memory in combination with interpolation.